The invention concerns chains for moving loads, termed rigid chains, and more particularly the links used to form such chains.
Rigid chains, also known as articulated rods, can go from a folded state in which they occupy a small overall size to a deployed state in the form of a rectilinear and rigid structure capable of pulling, supporting and pushing heavy loads.
Such chains are formed by a series of analogous links, each link comprising two lateral flanges, sometimes termed flanks, mounted in rotation from one link to another by means of rotation pins. The links are such that the chain can go from a rectilinear state to a curved state or a state rolled up on itself and vice versa. The chain can be curved in a single plane and in a single direction. Curvatures in other directions and twists are prevented, in particular by an appropriate configuration and an appropriate adjustment of the parts constituting the chain.
In FR 2 134 196, each link flange is produced by assembling two different mechanical parts. A flat first part of complex shape transmits compression forces from one link to another when the chain is rectilinear. A flat second part of oblong shape connects two adjacent rotation pins and operates essentially in traction. The two parts are assembled against one another by crimping them. A manufacturing defect, for example a flatness defect, sometimes occurs in a part. A defect of this kind may be tolerable at the scale of the link. In other words, the operation of the chain is not compromised if a link of the chain feature a minimal defect. Now these parts are generally mass produced, in batches. If a defect, even a minimal defect, is reproduced on each of the parts of a batch used to form a chain, these defects are cumulative over the length of the chain to the point of preventing its correct operation, in particular over great lengths. Moreover, in the case of a bending force oriented substantially perpendicularly to the flanges, the crimping and/or the flatness of the flanges may be degraded to the point of bending of one of the flanks and immobilization of the chain.
FR 2 573 832 describes an embodiment in which a one-piece part is used to form each flange of the chain. Such parts are also subject to bending in the event of a bending force perpendicular to the flanges, which limits the conditions of use of the chain. Moreover, the length of the chain remains limited because of the risk of failures caused by manufacturing defects in a batch of parts.
The configuration described in FR 2 345 626 is simplified: the flange of the chain is constituted of only one type of part. For each flange of the chain, two rows of parts are superposed in a quincunx arrangement. The chain is also fragile in the event of bending forces oriented perpendicularly to the flanges.
The Applicant has developed rigid chains the flanges of which are produced by assembling identical flat parts. A configuration of this kind is described in FR 2 786 476. The manufacture and the assembly of the parts are facilitated. In this configuration, the quincunx superposition of two identical parts for each flange is still necessary. This superposition is difficult to preserve over time, in particular in the event of bending forces perpendicular to the plane of the flanges. Play and relative movements that are not wanted occur between the parts of a flank of the chain. Such play can lead to premature wear, or even to bending of the chain.
The invention improves on the situation.